1. Field of the Invention
This invention relates generally to efficient means for the generation of electrical power or other power utilizing energy from geothermal sources, and more specifically relates to arrangements including efficient steam generation and pumping equipment for application in deep hot wells for transfer of thermal energy to the earth's surface.
2. Description of the Prior Art
A major advance in the art of extraction and use of geothermal energy is described in U.S. Pat. No. 3,824,793, entitled "Geothermal Energy System and Method", by H. B. Matthews, issued July 23, 1974 and assigned to the applicant's assignee. The prior Matthews invention provides means for efficient power generation employing energy derived from subterranean geothermal sources through the generation of substantially dry super-heated steam and the consequent operation of sub-surface equipment for pumping extremely hot well water at high pressure to the earth's surface. Clean water is injected at a first or surface station into the deep well where thermal energy stored in hot solute-bearing deep well water is used in a boiler at a second or deep well station to generate super-heated steam from the clean water. The resultant substantially dry super-heated steam is used at the well bottom for operating a turbine driven pump for pumping the hot solute bearing well water to the first station at the earth's surface, the water being pumped at all times and locations in the system at pressures which prevent flash steam formation. The highly energetic water is used at the surface or first station in a binary fluid system so that its thermal energy is transferred to a closed-loop surface-located boiler-turbine system for driving an electrical power alternator. Cooled, clean water is regenerated by the surface system for re-injection into the well for operation of the steam turbine therein. Undesired solutes are pumped back into the earth via a separate well in the form of a concentrated brine.
A turbine pump unit well adapted for use with the above described geothermal energy conversion system is described in U.S. Pat. No. 3,908,380, entitled "Geothermal Energy Turbine and Well System" By J. L. Lobach, issued Sept. 30, 1975 and assigned to the applicant's assignee. The turbine driven pump features a compact and efficient system turbine configuration adapted for use in the hostile environment of the deep hot-water well. Substantially dry super-heated steam from the boiler passes downwardly to impact turbine blades at the periphery of the turbine wheel. A further feature permits the expanding steam then to reverse its sense of flow in a compact arrangement returning the steam along the axis of the turbine wheel and then to the earth's surface for further energy recovery.
The quality of the steam at the turbine inlet of the turbine pump unit, however, may vary depending on the particular geometry of the boiler annulus and on other factors affecting the heat transfer rates. Under certain conditions the boiler may be able to generate wet steam only, causing the turbine efficiency, the total turbine power output, and the turbine service life to decrease from their design values. For example, the presence of liquid droplets in the incoming high velocity steam will cause corrosion in the turbine and will cause the potentially destructive electro-static charge build-up on the rotating assembly due to the polar nature of the water droplets.
An apparatus which helps to alleviate the problems associated with wet steam is described in co-pending U.S. patent application, Ser. No. 274,838, filed June 9, 1981 entitled "Downhole Liquid Trap For A Geothermal Pumping System", by Andrej M. R. Aplenc, and assigned to Sperry Corporation. The above referenced invention is coupled to the turbine driven pumping equipment which is responsive to the superheated steam emitted from the boiler. The liquid droplets entrained in steam are separated from the vapor by either centrifugal, gravitational, or inertial separation means. The droplets are collected in a liquid trap, and the vapor is directed into the inlet of the turbine driven pumping equipment. The liquid collected in the trap may be harmlessly flashed back into the exhaust vapor of the turbine driven pumping equipment, thereby enabling the turbine driven pumping equipment to operate more efficiently and preventing damage to the turbine. There are, however, no provisions within the liquid trap to vaporize the separated out liquid other than by flashing it back into the exhaust vapor. Moreover, even though the separated out steam is of very high quality, it is not completely dry and there are no provisions within the liquid trap to superheat it.